Dithiodiglycol (otherwise referred to as DIHEDS, di-hydroxyethyl disulfide, 2,2′-dithiodiethanol or DTDG) is a well-known article of commerce, being used as a chemical intermediate in the manufacture of many useful compounds, such as lubricant additives.
In general, disulfides can be produced by the oxidation of the corresponding mercaptan with an oxidizing agent, such as sulfur or oxygen. Most alkyl disulfides have low to negligible water solubility. For the production of these alkyl disulfides, removal of water is a simple matter of phase separation of the water from the disulfide. However, dithiodiglycol is miscible with water.
In the production of dithiodiglycol, excess β-mercaptoethanol (otherwise referred to as BME or 2-mercaptoethanol) is frequently used to increase the production of disulfides as compared to trisulfides. The excess β-mercaptoethanol at the end of the reaction has proven to be particularly difficult to remove by any single physical means, including vacuum stripping or wiped film evaporation. Distillation of dithiodiglycol as an overhead-product is difficult, because it has a boiling point of 163° C. at 3 torr. Prolonged heating of dithiodiglycol can produce decomposition and significant discoloration of the material.
There is a need in the art for an improved method of making dithiodiglycol with low residual β-mercaptoethanol, low residual water, and low alkyl trisulfide content.